An Introduction to Aerosols

Pasquier

et al. 2022

Preprint

Abstract. Mixed-phase clouds (MPCs) can have a net warming or cooling radiative effect on climate inﬂuenced by the phase and concentration of cloud particles. They have received considerable attention due to high spatial coverage and occurrence frequency in the Arctic. To initiate ice formation in MPCs at temperatures above −38 °C, ice nucleating particles (INPs) are required, which therefore have important implications on the radiative properties of MPCs by altering the ice to liquid ratio of hydrometeors. As a result, constraining ambient INP concentrations could promote accurate representation of cloud microphysical processes and reduce the uncertainties in estimating the cloud-phase-related climate feedback in climate models. Currently, INP parameterizations are lacking for remote Arctic environments. Here we present INP number concentrations and their variability measured in Ny-Ålesund (Svalbard) at temperatures between 0 and −30 °C. No distinguishable seasonal difference was observed from 12 weeks of ﬁeld measurements in autumn 2019 and spring 2020. In addition, correlating INP concentrations to aerosol physical properties was not feasible. Therefore, we propose a lognormal-distribution-based parameterization to predict Arctic INP concentration solely as a function of temperature. In practice, the parameterized variables allow for a) the prediction of the most likely INP concentrations and; b) the retrieval of the governing distribution of INP concentrations at given temperatures in the Arctic.

Section: Aerosol Physical Property Measurementsmentioning

confidence: 99%

Predicting atmospheric background number concentration of ice nucleating particles in the Arctic

Pasquier

et al. 2022

Preprint

“…Downstream, an Aerodynamic Particle Sizer Spectrometer (APS; Model 3321, TSI Inc., US) and a Scanning Mobility Particle Sizer Spectrometer (APS; Model 3938, TSI Inc., US) recorded aerosol size distributions between approximately 10 nm and 20 µm. In this study, aerodynamic diameter and electronic mobility were converted to physical diameter assuming a shape factor χ = 1.2 and an assumed particle density ρ = 2 g cm −3 (Thomas and Charvet, 2017). Ambient aerosol was collected over a time span of 20 minutes into pure water (15 mL, W4502-1L, Sigma-Aldrich, US) for offline INP analysis using high flow-rate impingers (Coriolis ® µ, Bertin Instruments, France, 300 L min −1 ) attached to the end of the inlets .…”

Section: In Situ Aerosol and Inp Measurementsmentioning

confidence: 99%

Retrieving ice nucleating particle concentration and ice multiplication factors using active remote sensing validated by in situ observations

Ihn

Mignani

et al. 2022

Preprint

Abstract. Understanding the evolution of the ice phase within mixed-phase clouds (MPCs) is necessary to reduce uncertainties related to the cloud radiative feedback in climate projections and precipitation initiation. Both primary ice formation via ice nucleating particles (INPs) and secondary ice production (SIP) within MPCs are unconstrained, not least because of the lack of atmospheric observations. In the past decades, advanced remote sensing methods have emerged which provide high resolution data of aerosol and cloud properties and could be key in understanding microphysical processes on a global scale. In this study, we retrieved INP concentrations, and ice multiplication factors (IMFs) in wintertime orographic clouds using active remote sensing and in situ observations obtained during the RACLETS campaign in the Swiss Alps. INP concentrations in air masses dominated by Saharan dust and continental aerosol were retrieved from a polarization Raman lidar and validated with aerosol and INP in situ observations on a mountaintop. A calibration factor of 0.0204 for the global INP parameterization by DeMott et al. (2010) is derived by comparing in situ aerosol and INP measurements improving the INP concentration retrieval for continental aerosols. Based on combined lidar and radar measurements, the ice crystal number concentration and ice water content were retrieved and validated with balloon-borne in situ observations, which agreed with the balloon-borne in situ observations within an order of magnitude. For seven cloud cases the ice multiplication factors (IMFs), defined as the quotient of the ice crystal number concentration to the INP concentration, were calculated. The median IMF was around 80 and SIP was active (defined as IMFs > 1) nearly 85 % of the time. SIP was found to be active at all observed temperatures (−30 °C to −5 °C) with highest IMFs between −20 °C and −5 °C. The introduced methodology could be extended to larger datasets to better understand the impact of SIP not only over the Alps but also at other locations and for other cloud types.

“…At the lowest sampling line, a commercial Aerodynamic Particle Sizer Spectrometer (APS, Model 3321, TSI Corp., US) recorded size distributions continuously (see Figure 2e). Aerodynamic diameter was converted to physical diameter using a shape factor χ = 1.2 and an assumed particle density ρ = 2 g cm −3 (Thomas and Charvet, 2017).…”

Section: Aerosol and Inp Measurementsmentioning

confidence: 99%

Unveiling atmospheric transport and mixing mechanisms of ice nucleating particles over the Alps

Mignani

Schär

et al. 2021

Preprint

Abstract. Precipitation over the mid-latitudes originates mostly from the ice phase within mixed-phase clouds, signifying the importance of initial ice crystal formation. Primary ice crystals are formed on ice nucleating particles (INPs), which are sparsely populated in the troposphere. INPs are emitted by a large number of ground-based sources into the atmosphere, from where they can get lifted up to cloud heights. Therefore, it is vital to understand vertical INP transport mechanisms, which are particularly complex over orographic terrain. We investigate the vertical transport and mixing mechanisms of INPs over orographic terrain during cloudy conditions by simultaneous measurements of in situ INP concentration at a high valley and a mountaintop site in the Swiss Alps in late winter 2019. On the mountaintop, the INP concentrations were on average lower than in the high valley. However, a diurnal cycle in INP concentrations was observed at the mountaintop, which was absent in the high valley. The median mountaintop INP concentration equilibrated to the concentration found in the high valley towards the night. We found that in nearly 70 % of the observed cases INP-rich air masses were orographically lifted from low elevation upstream of the measurement site. In addition, we present evidence that over the course of the day air masses containing high INP concentrations were advected from the Swiss plateau towards the measurement sites, contributing to the diurnal cycle of INPs. Our results the local INP concentration enhancement over the Alps during cloud events.